1. Field of the Invention
The present invention pertains to an improvement in venting combustion gases in rocket motors. More particularly the present invention relates to an improved vented spacer to help equalize pressure between the inside and outside of the propellant grains inside rocket motors.
2. Description of the Related Art
Solid-propellant rocket motors are sometimes loaded with free-floating cartridge-loaded propellant grains to facilitate loading and reduce costs. These grains are not structurally adequate to support the pressure which results during combustion, so the pressure must be equalized between the inside and outside of the grain to prevent potentially catastrophic failures. One method of equalizing this pressure is to vent a small portion of the gases from inside the propellant grain to the annular space between the outside of the propellant grain and the rocket motor tube.
Since the combustion process is luminous and the gases created are extremely hot, over 4000xc2x0 F., venting combustion gases creates a danger of overheating the motor tube of a rocket motor by radiative and convective heating. There is also a danger of igniting the outside diameter of the propellant grain, a surface which was not intended to burn. Case heating and increased gas generation both cause failure of the case of the rocket motor, throwing extremely hot pieces of propellant and casing in all directions. Case heating is especially a problem when, in the interest of minimizing weight, aluminum is used for the motor case material.
Newer, less sensitive, more energetic propellants have higher flame temperatures than previous propellants. The higher operating temperatures increase the danger of overheating the rocket motor casing during the venting process. Therefore, the amount of heat permitted to reach the casing wall must be minimized. Unfortunately, the need to maximize the energy density of the rocket motor puts space at a premium. Thus, space for a venting arrangement is limited. This increases the difficulty in designing solutions to the problems set forth above.
In current cartridge-loaded rocket motors, a charge support spacer is used to vent combustion gases. In such a current device, a propellant grain is contained within a motor case. The propellant grain is sealed at the nozzle end of the motor. The charge support spacer is located between the end of the propellant grain and a spring which holds the propellant in place. A group of heat cups are placed around the springs to assist in protecting the portion of the casing surrounding the springs from heating from propellant gases. Although the heat cups provide some relief from heat generated during combustion, this relief is marginal, especially when a hotter propellant is used. The charge support spacer is comprised of two separated metal plates which separate the springs from the propellant and prevent the spring from embedding into the propellant. The current charge support spacer provides direct venting to an annulus between the inside of the motor case, outside the propellant grain and running back to the nozzle. The current spacer is made of sheet steel which permits radiative heating of the motor case, provides minimal contact area, and no ablative cooling.
Composite propellants have also been developed for use in rocket motors to improve performance and safety characteristics. Unfortunately with composite propellants, the heating of the rocket motor casing in the region of the charge support spacer charred and bulged the motor casing unacceptably. The present invention provides a solution to all of the problems described above.
The present invention comprises a direct replacement for the charge support spacer currently used in rocket motors as discussed above. The present invention comprises a vented spacer that cools combustion gases through contact, ablation, and expansion prior to equalizing pressure by transferring these gases from the inside of the propellant grain to the outside of the grain. The vented spacer also blocks the transfer of heat from the inside of the propellant to the rocket motor case by radiation. The gases are cooled to the point that they present no hazard to the rocket motor casing or the outer diameter of the propellant grain. The vented spacer accomplishes these tasks in the same amount of area as the charge support spacer.
Accordingly, it is the object of this invention to provide a device which cools combustion gases in a rocket motor and blocks radiation to prevent damage to the outside of the propellant grain or the motor case.
It is a further object of this invention to provide a device to equalize pressure between the inside and outside of propellant grain in a rocket motor while still providing the required support to the propellant grain.
This invention accomplishes these objectives and other needs related to improvement of venting combustion gases in a rocket motor.